1. Field of the Invention
The present invention relates to a focused ion beam (FIB) system for processing a specimen by directing a focused ion beam at the specimen and, more particularly, to a FIB system which calculates the processing conditions while the operator is monitoring the specimen after optical conditions are selected.
2. Description of Related Art
A FIB system is a tool for processing a specimen by sharply focusing an ion beam produced from an ion source and directing the beam at the specimen so as to etch it. Among applications of such FIB systems, etching techniques relying on FIB have become widely spread.
FIB systems using these techniques are widely used in defect analysis of semiconductor devices and specimen preparation in transmission electron microscopy as well as in micromachining. Especially, in three-dimensional analysis of semiconductor devices that has attracted the greatest attention, FIB systems are becoming indispensable tools.
FIG. 1 shows the structure of a FIB system. The inside of the body 1 of the system is evacuated. The body 1 has a specimen chamber 1a in which a specimen stage 3 is placed. A specimen 2, such as a semiconductor device, is placed on the stage 3. Also contained in the body 1 are an ion source 5 for producing an ion beam 4, an extraction electrode 6 for extracting ions from the ion source 5, accelerating electrodes 7, condenser lenses 8 for focusing the ion beam, beam-blanking electrodes 9, multiple variable apertures 10, beam-deflecting electrodes 11 for scanning the ion beam in two dimensions, and an objective lens 12. A detector 13 for detecting secondary charged particles produced from the specimen 2 is also installed in the specimen chamber 1a. Electrostatic lenses are used for the condenser lenses 8 and objective lens 12.
Some components (e.g., condenser lenses 8, multiple variable apertures 10, beam-deflecting electrodes 11, and objective lens 12) of the body 1 of the FIB system are driven by a FIB driver portion 14 that is under control of a computer 15. The computer 15 has an arithmetic unit 16, an input device 17, and a monitor 18 (e.g., a cathode-ray tube (CRT) or liquid crystal display (LCD)). The arithmetic unit 16 has RAM and HDD which are incorporated therein or attached thereto.
For example, where the amount of current of the ion beam hitting the specimen 2 is varied, the FIB driver portion 14 controls the condenser lenses 8 and objective lens 12 to control the intensities of the lenses. This varies the degree of focusing of the beam. An appropriate aperture is selected from the multiple variable apertures 10 mounted in the optical path of the ion beam 4. In this way, the amount of the passing ion beam is controlled. Where the ion beam 4 is scanned over the specimen 2 in two dimensions or raster-scanned, a scan signal is supplied to the beam-deflecting electrodes 11 from the FIB driver portion 14.
The specimen 2 is placed on the specimen stage 3. The stage 3 is designed to be capable of being moved in two dimensions within a horizontal plane, rotated, and tilted by a stage control portion 19, which is under control of computer 15.
Ions are extracted from the ion source 5 by the extraction electrode 6. The ions are accelerated by the accelerating electrodes 7. The ion beam 4 of the accelerated ions is sharply focused onto the specimen 2 by the condenser lenses 8 and objective lens 12. The beam position on the specimen 2 is scanned by supplying the scan signal to the beam-deflecting electrodes 11. As a result, a desired portion of the specimen is cut or processed by the ion beam.
The intensity of the ion beam 4 is controlled by the computer 15 via the FIB driver portion 14 such that the specimen 2 is not processed. The beam is scanned over the specimen 2 in two dimensions. Secondary electrons emanating from the specimen 2 are detected by the secondary electron detector 13. Image processing is performed by the arithmetic unit 16 of the computer 15 and then a secondary electron image is displayed on the monitor 18.
Today, dual-beam systems each consisting of a conventional in-line scanning electron microscope (SEM) to which FIB capabilities are added have also become widespread. The dual-beam systems are described, for example, in Japanese Patent Laid-Open No. H7-37538.
A dual-beam system (FIB/SEM instrument) is a combined instrument capable of playing the role of the conventional FIB instrument that etches a specimen as a semiconductor defect analysis tool and then moves the specimen onto a SEM to observe the specimen.
This combined instrument has the advantage that it can perform SEM imaging similarly to an ordinary, single-function FIB machine. That is, an ion beam is directed at the top surface of a specimen. A desired portion is etched. After completion of the etching, the etched cross section can be immediately observed as an SEM image without moving the specimen. As a result, the combined instrument exhibits excellent capabilities in defect analysis and shortens the process sequence time. Concomitantly, the yield management can be done at an improved rate. Furthermore, the combined instrument has a small footprint because of the combined capabilities. The cost can also be reduced.
The above-described FIB/SEM instrument roughly consists of a FIB control portion, a SEM control portion, and a stage control portion for controlling a specimen stage. These portions are controlled by a computer. The FIB instrument etches a specimen by directing an ion beam at the specimen such that the beam impinges on the specimen normally from vertically above it under the control of the computer. In the SEM, an electron beam impinges on the cross section of the formed hole at an angle of 30° with respect to the specimen surface to permit observation of the cross-sectional morphology.
Where milling is done by a FIB system, it has been heretofore necessary to manually set parameters or select an appropriate setting file and utilize it. The parameters include (1) the size of the processed region, (2) the intensity of the used ion beam, (3) the depth of the cut hole and the kind of the specimen or the dose of the illuminating ion beam, and (4) processing and scanning conditions (dwell time (DT) per hit point and the dwell point spacing (DPS)).
However, manual setting of the parameters (1)-(4) above or selection of an appropriate setting file depends on the knowledge and experience of each individual operator of the FIB system. Therefore, much labor and time are required to set the parameters. Furthermore, if different operators set different parameters in processing the same material, different processing results will arise. In addition, if any set parameter is disabled because of the hardware limitation, the settings are invalidated.